Portable drag compressor powered mechanical ventilator

ABSTRACT

A ventilator device and system comprising a rotating compressor, preferably a drag compressor, which, at the beginning of each inspiratory ventilation phase, is accelerated to a sufficient speed to deliver the desired inspiratory gas flow, and is subsequently stopped or decelerated to a basal flow level to permit the expiratory ventilation phase to occur. The ventilator device is small and light weight enough to be utilized in portable applications. The ventilator device is power efficient enough to operate for extended periods of time on internal or external batteries. Also provided is an oxygen blending apparatus which utilizes solenoid valves having specific orifice sizes for blending desired amounts of oxygen into the inspiratory gas flow. Also provided is an exhalation valve having an exhalation flow transducer which incorporates a radio frequency data base to provide an attendant controller with specific calibration information for the exhalation flow transducer.

This application is a division of application Ser. No. 08/324,172, filedOct. 14, 1994, now abandoned.

FIELD OF THE INVENTION

The present invention pertains generally to medical equipment and moreparticularly to a compressor powered mechanical ventilator device fordelivering respiratory ventilation to a mammalian patient.

BACKGROUND OF THE INVENTION A. Principles of Mechanical Ventilation

In many clinical settings mechanical ventilators are used to facilitatethe respiratory flow of gas into and out of the lungs of patients whoare sick, injured or anesthetized.

In general, mechanical ventilators provide a repetitive cycling ofventilatory flow, each such repetitive cycle being separated into twophases--an inspiratory phase followed by an expiratory phase.

The inspiratory phase of the ventilator cycle is characterized by themovement of positive-pressure inspiratory flow of gas through theventilator circuit and into the lungs of the patient. The expiratoryphase of the ventilatory cycle is characterized by cessation of thepositive pressure inspiratory flow long enough to allow lung deflationto occur. The exhaled gas is vented from the ventilator circuit,typically through an exhalation valve. In patient whose lungs andthoracic musculature exhibit normal compliance, the act of exhalation isusually permitted to occur spontaneously without mechanical assistancefrom the ventilator.

It is sometimes desirable to control the airway pressure duringexhalation to maintain a predetermined amount of positive back pressureduring all, or a portion of, the respiratory cycle. Such techniques areoften utilized to treat impairments of lung capacity due to pulmonaryatelectasis or other factors.

The mechanical ventilators of the prior art have been grouped undervarious classification schemes, based on various criteria. In general,mechanical ventilators may be grouped or classified according to theparameter(s) which are utilized for a) triggering, b) limiting and c)terminating (e.g., cycling) the inspiratory phase of the ventilatorcycle.

"Triggering" is the action that initiates the inspiratory phase of theventilator cycle. The initiation of the inspiratory phase may betriggered by the ventilator or the patient. The variables and/orparameters which are utilized to trigger the beginning of theinspiratory phase include: time (i.e., respiratory rate), thecommencement of spontaneous inhalation by the patient and/orcombinations thereof.

"Limiting" of the inspiratory phase refers to the manner in which theinspiratory gas flow is maintained within prescribed ranges to optimizethe ventilation of the patient's lungs. The limiting variables and/orparameters are typically controlled by the ventilator, but may change asa result of patient effort and/or physiologic variables such as lungcompliance and airway resistance. The variables and/or parameters whichare utilized for limiting the inspiratory phase include flow rate,airway pressure and delivered volume.

"Terminating" or "cycling" of the inspiratory phase of the ventilatorcycle refers to the point at which the inspiratory flow is stopped andthe ventilator and/or patient are permitted to "cycle" into theexpiratory phase. Depending on the ventilator control settings, thetermination of the inspiratory phase may be brought about by theventilator or the patient. The variables and/or parameters which areutilized to terminate the inspiratory phase include: time; peak airwaypressure; and/or tidal volume (V_(t)).

B. Mechanical Ventilation Modes Utilized In Modern Clinical Practice

In addition Mechanical ventilators are utilized to deliver various"modes" of mechanical ventilation, the particular mode of ventilationbeing selected or prescribed based on the clinical condition of thepatient and the overall objective (i.e., long term ventilation, shortterm ventilation, weaning from ventilator, etc. . . . ) of themechanical ventilation.

I. Ventilation Modes

i. Intermittent Mandatory Ventilation (IMV)

Intermittent Mandatory Ventilation is a ventilation mode wherein aspontaneously breathing patient receives intermittent mechanicalinflation supplied asynchronously by the ventilator.

ii. Synchronized Intermittent Mandatory Ventilation (SMIV)

Synchronized Intermittent Mandatory Ventilation is a ventilation modewherein a spontaneously breathing patient receives occasional mandatoryventilatory breaths. Mandatory ventilator breaths are synchronized withthe patient's spontaneous inspiratory efforts.

iii. Controlled Mechanical Ventilation (CMV)

Controlled Mechanical Ventilation (CMV) is a ventilation mode whereinmechanical breaths are delivered to the patient at time intervals whichare unaffected by patient efforts. Controlled Mechanical Ventilation istypically utilized in patients who are not breathing spontaneously.

iv. Assist/Control Ventilation (A/C)

Assist/Control Ventilation (A/C) is a ventilation mode wherein thepatient is able to volitionally alter the frequency of mandatoryventilator breaths received, but can not alter the flow and title volume(V_(t)) of each ventilator breath received. Controlled, mandatorybreaths are initiated by the ventilator based on the set breath rate. Inaddition, the patient can demand and trigger an assist breath. Aftersuccessful triggering of an assist breath, the exhalation valve isclosed and gas is delivered to the patient to satisfy the preset tidalvolume, peak flow and wave form.

C. Breath Types Utilized in Modern Clinical Practice

Breath types are typically classified according to the particularfunctions which control:

a) triggering;

b) limiting; and

c) cycling of each breath delivered by the mechanical ventilator, asdescribed and defined hereabove.

Typical breath types and ventilator parameters utilized in modernclinical practice include the following:

i. Machine-Cycled--Mandatory Breath

A machine-cycled, mandatory breath is a breath that is triggered,limited and cycled by the ventilator.

ii. Machine-Cycled--Assist Breath

A machine cycled assist breath is a breath that is triggered by thepatient, but is limited and cycled by the ventilator.

iii. Patient-Cycled--Supported Breath

A patient-cycled, supported breath is a breath that is triggered by thepatient, limited by the ventilator, and cycled by the patient.

iv. Patient-Cycled--Spontaneous Breath

A patient-cycled spontaneous breath is a breath that is triggered,limited and cycled by the patient. While patient effort limits the flow,and hence the inspiratory volume of the breath, the ventilator may alsolimit the breath by providing a flow that is to low to maintain aconstant pressure in the face of patient inspiratory demand.

v. Volume-Controlled Mandatory Breaths

Volume-controlled breaths are machine-triggered mandatory breaths. Theinspiratory phase is initiated by the ventilatory based on a presetbreath rate. The inspiratory phase is ended, and the expiratory phasebegun, when the breath delivery is determined to be complete based on apreset tidal volume, peak flow and wave form setting. The ventilatorremains in expiratory phase until the next inspiratory phase begins.

vi. Volume-Controlled--Assist Breaths

Volume-controlled breaths are machine cycled supported breaths that areinitiated by the patient. Volume-controlled assist breaths may beinitiated only when the "assist window" is open. The "assist window" isthe interval or time during which the ventilator is programmed tomonitor inspiratory flow for the purpose of detecting patientinspiratory effort. When a ventilator breath is triggered, theinspiratory phase of such breath will continue until a preset tidalvolume peak flow and wave form have been achieved. Thereafter, theexhalation valve is open to permit the expiratory phase to occur. Theventilatory remains in the expiratory phase until the nextpatient-triggered breath, or the next mandatory inspiratory phase,begins.

vii. Pressure-Controlled Breaths

Pressure-Controlled breaths are delivered by the ventilator usingpressure as the key variable for limiting of the inspiratory phase.During pressure control, both the target pressure and the inspiratorytime are set, and the tidal volume delivered by the ventilator is afunction of these pressure and time settings. The actual tidal volumedelivered in each pressure-controlled breath is strongly influenced bypatient physiology.

viii. Pressure Support Breaths

Pressure support breaths are triggered by the patient, limited by theventilator, and cycled by the patient. Thus, each breath is triggered bypatient inspiratory effort, but once such triggering occurs theventilator will assure that a predetermined airway pressure ismaintained through the inspiratory phase. The inspiratory phase ends,and the expiratory phase commences, when the patients inspiratory flowhas diminished to a preset baseline level.

ix. Sigh Breaths

A sigh breath is a machine-triggered and cycled, volume-controlled,mandatory breath, typically equal to 1.5 times the current tidal volumesetting. The inspiratory phase of each sigh breath delivers a presettidal volume and peak flow. The duration of the inspiratory phase ofeach sigh breath is limited to a maximum time period, typically 5.5seconds. The ventilator may be set to deliver a sigh functionautomatically after a certain number of breaths or a certain timeinterval (typically 100 breaths for every 7 minutes), which everinterval is shorter. The sigh breath function it may be utilized duringcontrol, assist and SIMV modes of operation, and is typically disabledor not utilized in conjunction with pressure controlled breath types orcontinuous positive air way pressure (CPAP).

x. Proportional Assist Ventilation (PAV)

Proportional Assist Ventilation (PAV) is a type of ventilator breathwherein the ventilator simply amplifies the spontaneous inspiratoryeffort of the patient, while allowing the patient to remain in completecontrol of the tidal volume, time duration and flow pattern of eachbreath received.

xi. Volume Assured Pressure Support (VAPS)

Volume Assured Pressure Support (VAPS) is a type of ventilator breathwherein breath initiation and delivery is similar to a pressure supportbreath. Additionally, the ventilator is programmed to ensure that apreselected tidal volume (V_(t)) is delivered during such spontaneouslyinitiated breath.

D. Oxygen Enrichment Of The Inspiratory Flow

It is sometimes desirable for mechanical ventilators to be equipped withan oxygen-air mixing apparatus for oxygen enrichment of the inspiratoryflow. Normal room air has an oxygen content (FiO₂) of 21%. In clinicalpractice, it is often times desirable to ventilate patients with oxygenFiO₂ from 21% to 100%. Thus, it is desirable for mechanical ventilatorsto incorporate systems for blending specific amounts of oxygen withambient air to provide a prescribed oxygen-enriched FiO₂. Typically,volume-cycle ventilators which utilize a volume displacement apparatushave incorporated oxygen mixing mechanisms whereby compressed oxygen iscombined with ambient air to produce the selected FiO₂ as both gases aredrawn into the displacement chamber during the expiratory phase of theventilator cycle. Nonbellows-type volume-cycled ventilators haveincorporated other air-oxygen blending systems for mixing the desiredrelative volumes of oxygen and air, and for delivering such oxygen-airmixture through the inspirations circuitry of the ventilator.

E. Regulation/Control Of Expiratory Pressure

The prior art has included separately controllable exhalation valveswhich may be preset to exert desired patterns or amounts of expiratoryback pressure, when such back pressure is desired to prevent atelectasisor to otherwise improve the ventilation of the patient.

The following are examples of expiratory pressure modes which arefrequently utilized in clinical practice:

i. Continuous Positive Airway Pressure (CPAP)

Continuous Positive Airway Pressure (CPAP) is employed during periods ofspontaneous breathing by the patient. This mode of ventilation ischaracterized by the maintenance of a continuously positive airwaypressure during both the inspiratory phase, and the expiratory phase, ofthe patient's spontaneous respiration cycle.

ii. Positive End Expiratory Pressure (PEEP)

In Positive End Expiratory Pressure a predetermined level of positivepressure is maintained in the airway at the end of the expiratory phaseof the cycle. Typically, this is accomplished by controlling theexhalation valve so that the exhalation valve may open only until thecircuit pressure has decreased to a preselected positive level, at whichpoint the expiration valve closes again to maintain the preselectedpositive end expiratory pressure (PEEP).

F. Portable Ventilators of the Prior Art

The prior art has included some non-complex portable ventilators whichhave inherent limitations as to the number and type of variables and/orparameters which may be utilized to trigger, limit and/or terminate theventilator cycle. Although such non-complex ventilators of the prior artare often sufficiently power efficient and small enough for portableuse, their functional limitations typically render them unsuitable forlong term ventilation or delivery of complex ventilation modes and orbreath types.

The prior art has also included non-portable, complex microprocessorcontrolled ventilators of the type commonly used in hospital intensivecare units. Such ventilators typically incorporate a microcomputercontroller which is capable of being programmed to utilize variousdifferent variables and/or parameters for triggering, limiting andterminating the inspiratory phase of the ventilator cycle. Complexventilators of this type are typically capable of delivering manydifferent ventilation modes and or breath types and are selectivelyoperable in various volume-cycled, pressure cycled or time-cycled modes.However, these complex ventilators of the prior art have typically beentoo large in size, and too power inefficient, for battery-drivenportable use. As a result of these factors, most of the complexmicro-processor controlled ventilators of the prior art are feasible foruse only in hospital critical care units.

As is well known there exist numerous settings, outside of hospitalcritical care units, where patients could benefit from the availabilityof a small, battery powered, complex microprocessor controlledmechanical ventilator capable of delivering extended modes ofventilation. For example, critically ill patients sometimes requiretransport outside of the hospital in various transport vehicles, such asambulances and helicopters. Also, critical care patients are sometimestransiently moved, within the hospital, from the critical care unit tovarious special procedure areas (e.g., radiology department, emergencyroom, catheterization lab etc.) where they may undergo diagnostic ortherapeutic procedures not available in the critical care unit.Additionally, patients who require long term ventilation are not alwayscandidates for admission to acute care hospital critical care units ormay be discharged to stepdown units or extended care facilities. Also,some nonhospitalized patients may require continuous or intermittentventilatory support. Many of these patients could benefit from the useof complex microprocessor controlled ventilators, but may be unable toobtain such benefit due to the non-feasibility of employing suchventilators outside of the hospital-critical care unit environment.

In view of the foregoing limitations on the usability of prior artcomplex microprocessor controlled volume-cycled ventilators, thereexists a substantial need in the art for the development of a portable,highly efficient, ventilator capable of programmed delivery of variousmodern ventilatory modes and breath types, while also being capable ofuse outside of the hospital critical care unit environment, such as intransport vehicles, extended care facilities and patients homes, etc.

U.S. Pat. No. 4,493,614 (Chu et al.) entitled "PUMP FOR A PORTABLEVENTILATOR" describes a reciprocating piston pump which is purportedlyusable in a portable ventilator operable on only internal or externalbattery power.

U.S. Pat. No. 4,957,107 (Sipin) entitled "GAS DELIVERY MEANS" describesa rotating drag compressor gas delivery system which is ostensibly smallenough to be utilized in a portable ventilator. The system described inU.S. Pat. No. 4,957,107 utilizes a high speed rotary compressor whichdelivers a substantially constant flow of compressed gas. The rotarycompressor does not accelerate and decelerate at the beginning and endof each inspiratory phase of the ventilator cycle. Rather, the rotatingcompressor runs continuously, and a diverter valve is utilized toalternately direct the outflow of the compressor a) into the patientslungs during the inspiratory phase of the ventilation cycle, and b)through an exhaust pathway during the expiratory phase of theventilation cycle.

Thus, there remains a substantial need for the development of animproved portable mechanical ventilator which incorporates the followingfeatures:

A. Capable of operating for extended periods (i.e., at least 21/2 hours)using a single portable battery or battery pack as the sole powersource;

B. Programmable for use in various different ventilatory modes, such asthe above-described IMV, SMV, CMV, PAV, A/C and VPAS.

C. Usable to ventilate non-intubated mask patients as well as intubatedpatients.

D. Oxygen blending capability for delivering oxygen-enriched inspiratoryflow.

E. Capable of providing controlled exhalation back pressure for CPAP orPEEP.

F. Portable, e.g., less than 30 lbs.

SUMMARY OF THE INVENTION

The present invention specifically addresses the above referenceddeficiencies and needs of the prior art by providing comprises amechanical ventilator device which incorporates a rotary compressor fordelivering intermittent inspiratory gas flow by repeatedly acceleratingand decelerating the compression rotor at the beginning and end of eachinspiratory phase. Prior to commencement of each inspiratory ventilationphase, the rotary compressor is stopped, or rotated at a basalrotational speed. Upon commencement of an inspiratory phase, the rotarycompressor is accelerated to a greater velocity for delivering thedesired inspiratory gas flow. At the end of each inspiratory phase, therotational velocity of the compressor is decelerated to the basalvelocity, or is stopped until commencement of the next inspiratoryventilation phase. A programmable controller is preferably incorporatedto control the timing and rotational velocity of the compressor.Additionally, the controller may be programmed to cause the compressorto operate in various modes of ventilation, and various breath types, asemployed in modern clinical practice.

Further in accordance with the present invention, there is provided anoxygen blending apparatus which may be utilized optionally with therotatable compressor ventilation device of the present invention. Theoxygen blending apparatus of the present invention comprises a series ofvalves having flow restricting orifices of varying size. The valves areindividually opened and closed to provide a desired oxygen enrichment ofthe inspiratory gas flow. The oxygen blending apparatus of the presentinvention may be controlled by a programmable controller associatedwith, or separate from, the ventilator controller.

Still further in accordance with the invention, there is provided anexhalation valve apparatus comprising a housing which defines anexpiratory flow path therethrough and a valving system for controllingthe airway pressure during the expiratory phase of the ventilationcycle. A pressure transducer monitors airway pressure during exhalationthe output of which is used by the controller to adjust the valvingsystem to maintain desired airway pressure.

In addition the present invention utilizes an exhalation flow transducerto accurately measure patient exhalation flow which may be utilized fordetermination of exhaled volume and desired triggering of inspiratoryflow. In the preferred embodiment, the exhalation flow transducer isintegrally formed with the exhalation valve, however, those skilled inthe art will recognize that the same can be a separate componentinsertable into the system. To insure transducer performance accuracy,in the preferred embodiment, the particular operational characteristicsof each flow transducer are stored within a memory device preferably aradio-frequency transponder mounted within the exhalation valve totransmit the specific calibration information for the exhalation flowtransducer to the controller. Further, the particular construction andmounting of the flow transducer within the exhalation valve isspecifically designed to minimize fabrication inaccuracies.

Further objects and advantages of the invention will become apparent tothose skilled in the art upon reading and understanding of the followingdetailed description of preferred embodiments, and upon consideration ofthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a basic schematic diagram of a preferred ventilator system ofthe present invention incorporating, a) a rotary compressor ventilatordevice, b) an optional air-oxygen blending apparatus; and c) acontrollable exhalation valve, and d) a programmable controller orcentral processing unit (CPU) which is operative to control andcoordinate the functioning of the ventilator, oxygen blending apparatusand exhalation valve.

FIG. 2 is a detailed schematic diagram of a ventilator system of thepresent invention.

FIG. 3 is a front view of the control panel of a preferred ventilatorsystem of the present invention.

FIG. 4 is a perspective view of a preferred drag compressor apparatuswhich may be incorporated into the ventilator system of the presentinvention.

FIG. 5 is a longitudinal sectional view through line 5--5 of FIG. 4.

FIG. 6 is an enlarged view of a segment of FIG. 5.

FIG. 7 is an enlarged view of a segment of FIG. 6.

FIG. 8 is an elevational view of a preferred drag compressor componentof a mechanical ventilator device of the present invention.

FIG. 9 is a perspective view of the drag compressor component of FIG. 8.

FIG. 10 is an enlarged view of a segment of FIG. 9.

FIG. 11a is a longitudinal sectional view of a preferred exhalationvalve of the present invention.

FIG. 11b is a perspective view of the preferred spider bobbin componentof the exhalation valve shown in FIG. 11a.

FIG. 11c is an exploded perspective view of a portion of the exhalationvalve of FIG. 11a.

FIG. 11d is a perspective view of a portion of the exhalation valveshown in FIG. 11c.

FIG. 11e is an exploded perspective view of the preferred flowrestricting flapper component of the exhalation valve shown in FIGS.11a-11d.

FIG. 12 is a graphic example of flow vs. speed vs. pressure datagenerated for a preferred exhalation valve of the present invention,accompanied by an exhalation valve characterization algorithm computedtherefrom.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The following detailed description and the accompanying drawings areprovided for purposes of describing and illustrating a presentlypreferred embodiment of the invention and are not intended to describeall embodiments in which the invention may be reduced to practice.Accordingly, the following detailed description and the accompanyingdrawings are not to be construed as limitations on the scope of theappended claims.

A. General Description of the Preferred Ventilator System

With reference to FIGS. 1-2, the mechanical ventilation system 10 of thepresent invention generally comprises a) a programmable microprocessorcontroller 12, b) a ventilator device 14, c) an optional oxygen blendingapparatus 16 and d) an exhalation valve apparatus 18. Which ispreferably implemented as a portable, battery powered system.

The ventilator device 14 incorporates a rotating drag compressor 30which is driven by an electric motor 102. In response to control signalsreceived from controller 12, a bladed rotor within the compressor 30will undergo rotation for specifically controlled periods of timeand/or, within specifically controlled parameters, so as to provideinspiratory gas flow through line 22 to the patient PT.

The controller 12 comprises a programmable microprocessor which iselectrically interfaced a) to the ventilator device 14 by way of controlline 13, b) to the optional oxygen blending apparatus 16 by way ofcontrol line 17, and c) to the exhalation valve 18 by way of controlline 19 and also by RF communication between flow transducer transponder(21) and transmitter/receiver (23). Preferably incorporated into theexhalation valve 18 as will be described in more detail infra.

The controller 12 is preferably programmed to utilize selectedparameters (e.g., time, flow rate, tidal volume (V_(t)), airwaypressure, spontaneous breath initiation, etc.) for triggering, limitingand cycling the inspiratory flow in accordance with the selectedventilatory mode or breath type.

At the end of each inspiratory flow cycle, the patient PT is permittedto exhale through exhalation valve 18. The flow rate or pressure of theexpiratory flow through exhalation valve 18 is controlled by varying thedegree of flow restriction within the exhalation valve 18, in responseto control signals received through line 19 from controller 12. Thisenables the exhalation valve 18 to be utilized to create a selectedexpiratory back pressure (e.g., CPAP, PEEP).

Optional oxygen blending apparatus 16 may be utilized to enrich theoxygen content of the inspiratory gas flow provided by the dragcompressor ventilator device 14. The preferred oxygen blending apparatus16 comprises a plurality of (preferably five (5)) solenoid valves 52,each having a specific sized flow restricting orifice. The solenoidvalves 52 are arranged in parallel between an oxygen inflow manifold 26and an oxygen outflow manifold 28. The controller 12 is programmed toopen and close the individual solenoid valves 52 for specific periods oftime so as to provide a metered flow of oxygen through oxygen outflowmanifold 28 and into accumulator 54. Ambient air is drawn throughconduit 24 and filter 50, into accumulator 54, where the ambient aircombines with the metered inflow of oxygen to provide an oxygen-enrichedinspiratory flow containing a prescribed oxygen concentration (FIO₂).

The presently preferred embodiment of the system 10 will operate whensupplied with voltage input within the range of 85-264 VAC at 50/60 Hz.

An AC power cord is preferably connectable to the system 10 to provideAC power input.

Additionally, the system 10 preferably includes an internal batterycapable of providing at least 15 minutes, and preferably 30 minutes, ofoperation. During internal battery operation, some non-essentialdisplays may be dimmed or disabled by the controller 12. The internalbattery is preferably capable of being recharged by AC power inputprovided through the AC power cable, or by a separate battery charger.The internal battery is preferably capable of being fully charged, froma no charged state, within 24 hours. The internal battery charge light306 shown on the panel of the preferred controller 12a may additionallyflash if desired during charging of the internal battery.

Also, the system may include an external battery or battery set capableof providing at least 2 hours of operation, and preferably capable ofproviding 4 to 8 hours of operation. During external battery use, somenon-essential displays may be dimmed or disabled by the controller 12.The battery or battery set is preferably capable of being recharged bydelivery of AC power through the AC power cable, or by a separatebattery charger. It is preferable that the external battery or batteryset be capable of being fully charged, from a no charged state within 24to 48 hours. The external battery charge light 310 on the panel of thepreferred controller 12a may additionally flash if desired duringcharging of the external battery or battery set.

B. The Preferred Controller Apparatus

It will be appreciated that the controller 12 of the ventilator system10 of the present invention will vary in complexity, depending on thespecific capabilities of the system 10, and whether or not the optionaloxygen blending apparatus 16 is incorporated.

FIG. 3 shows the control panel of a preferred controller apparatus 12awhich is usable in connection with a relatively complex embodiment ofthe ventilatory system 10, incorporating the optional oxygen blendingapparatus 16.

CONTROLS SETTINGS AND DISPLAYS

The specific control settings and displays which are included in thepreferred controller 12a, and the ways in which the preferred controller12a receives and utilizes operator input of specific control settings,are described herebelow:

1. Standby-Off Control

The ventilator system 10 incorporates a stand by/off switch (not shown)which turns the main power on or off. A group of indicator lights 300are provided on the face panel of the controller 12a, and are more fullydescribed herebelow under the heading "monitors". In general, the panelindicator lights include an "on" indicator 302 which becomes illuminatedwhen the ventilator is turned on. An AC power low/fail indicator light304 activates when the AC power cord is present and the voltage is outof a specified operating range. Upon sensing low or faulty AC power, thecontroller 12a will automatically switch the ventilator 14 to internalbattery power. The ventilator will continue to operate on internalbattery power until such time as power in the internal battery reaches aminimum level. When the power in the internal battery reaches a minimumlevel, the controller 12a will cause the internal battery light and/oraudible alarm 308 to signal that the internal battery is near depletion.

A separate external battery light and/or audible alarm 312 is alsoprovided. The external battery light and/or audible alarm will activatewhen the external battery is in use, and has a battery voltage which isout of the acceptable operation range. During this condition, thecontroller 12a will cause all non-essential displays and indicators toshut down.

When AC power is connected to the ventilator 14, but the ventilator isturned off, any internal or external batteries connected to theventilator will be charged by the incoming AC current. Internal batterycharge indicator light 306 and external battery charge indicator light306 and external battery charged indicator light 310 are provided, andwill blink or otherwise indicate charging of the batteries when suchcondition exists.

2. Mode Select

A mode select module 320 incorporates plural, preferably five (5) modeselect buttons 322, 324, 326, 328, 330. Mode select button 322 sets thesystem 10 for Assist Control (a/c). Mode select button 324 sets thesystem 10 for Synchronized Intermittent Mandatory Ventilation (SIV).Mode select button 326 sets the system for Continuous Positive AirwayPressure (CPAP).

Spare mode select buttons 328, 330 are provided to permit the controller12a to be programmed for additional specific ventilation modes such asvolume assured pressure support (VAPS) or proportional assistventilation. When the controller is programmed for additional specificventilation modes, select buttons 328, 330 may be correspondinglylabeled and utilized to set the ventilator 14 to deliver suchsubsequently programmed ventilation modes.

3. Tidal Volume

A digital tidal volume display 332, with corresponding tidal volumesetting button 332a are provided. When tidal volume setting button 332ais depressed, value setting knob 300 may be utilized to dial in aselected tidal volume. The tidal volume display 332 will then provide adigital display of the currently selected tidal volume value.

The typical range of setable tidal volumes is 25 ml-2000 ml.

4. Breath Rate

A digital breath rate display 334, with corresponding breath ratesetting button 334a is provided. When breath rate setting button 334a isdepressed, value setting knob 300 may be utilized to dial in the desiredbreath rate. Breath rate display 334 will thereafter display thecurrently selected breath rate.

The typical rage of selectable breath rates is 0 to 80 breaths perminute.

5. Peak Flow

A digital peak flow display 336, and corresponding peak flow settingbutton 336a are provided. When peak flow setting button 336a isdepressed, value setting knob 300 may be utilized to dial in the desiredpeak flow. The peak flow display 336 will, thereafter, provide a digitaldisplay of the currently selected peak flow.

The typical range of peak flow settings is 10 to 140 liters per minute.

6. Flow Sensitivity

A flow sensitivity digital display 338, and corresponding flowsensitivity setting button 338a are provided. When flow sensitivitysetting button 338a is depressed, value setting knob 300 may be utilizedto dial in the desired flow sensitivity setting. The flow sensitivitysetting display 338 will, thereafter, provide a digital display of thecurrently selected flow sensitivity setting.

The flow sensitivity setting determines the trigger level for initiationof volume and pressure-controlled assist breaths or pressure supportbreaths. The initiation of volitional inspiratory effort by the patientcreates a change in airway flow as determined by: (turbine biasflow)-(exhalation flow)=patient flow. Triggering occurs when the patientairway flow exceeds the sensitivity setting. The typical range ofselectable flow sensitivity settings is from one to ten liters perminute, or off.

Optionally, a fail safe feature may be incorporated whereby, if thepatients flow demand does not exceed the flow sensitivity setting, butthe airway pressure drops more than 5 cmH₂ O below the set PEEP level,and inspiratory cycle will be initiated and a breath will be deliveredbased on current mode and control settings.

7. PEEP/CPAP

A PEEP/CPAP digital display 340, with corresponding PEEP/CPAP settingbutton 340a are provided. When PEEP/CPAP setting button 340a isdepressed, the value setting knob 300 may be utilized to dial in thedesired PEEP/CPAP setting.

The current PEEP/CPAP setting sets the level of pressure in the patientcircuit that is maintained between the end of inspiration and the startof the next inspiration. It is also known as the "baseline" pressure.

The preferred range of PEEP/CPAP setting is 0 to 50 cmH₂ O.

8. Pressure Support

A pressure support digital display 342, and corresponding pressuresupport setting button 342a, are provided. When pressure support settingbutton 142a is depressed, value setting knob 300 may be utilized to dialin the desired pressure support setting.

The pressure support setting determines the inspiratory patient circuitpressure during a pressure support breath. This control sets thepressure support level above the baseline setting established by thePEEP/CPAP setting. The total delivered pressure equals the PEEP or CPAPvalue+pressure support.

The typical range of pressure support settings is from 1 to 60centimeters of water (cmH₂ O), or off.

9. FiO₂ (% O₂)

An FiO₂ digital display 348, and corresponding FiO₂ setting button 348a,are provided. When the FiO₂ setting button 348a is depressed, the valuesetting knob 300 may be utilized to dial in the desired fractionalpercentage of oxygen in the air/oxygen gas mixture that is delivered tothe patient PT and used for the bias flow. In response to the FiO₂setting, the controller 12 will issue control signals to the oxygenblending apparatus 16 to effect the preset FiO₂.

The preferred range of setable FiO₂ is between 0.21 and 1.0 (i.e.,21-100 percent oxygen).

10. Pressure Control (Optional)

A pressure control digital display 350, and corresponding pressurecontrol setting button 350a are provided. When the pressure controlsetting button 350a is depressed, the value setting knob 300 may beutilized to dial in the desired pressure control value.

The pressure control setting enables the system 10 to be utilized forpressure control ventilation, and determines the inspiratory pressurelevel during delivery of each pressure control breath. The pressurecontrol setting sets the pressure level above any PEEP.

It is preferable that the range of possible pressure control settings befrom 1 to 100 cmH₂ O.

11. Inspiratory Time (Optional)

An optional inspiratory time digital display 352, and correspondinginspiratory time setting button 352a may be provided. When theinspiratory time setting button 352a is depressed, the value setting of300 may be utilized to dial in the desired inspiratory time.

The set inspiratory time is the time period for the inspiratory phase ofa pressure control breath. Thus, this inspiratory time setting isnormally usable for pressure control ventilation.

It is preferable that the range of setable inspiratory times being from0.3 to 10.0 seconds.

12. Additional Displays/Settings

Additional digital displays 344, 346, 354, 356 and corresponding settingbuttons 344a, 346a, 354a, 356a are provided to permit the controller 12to be subsequently programmed or expanded to receive and displayadditional control settings beyond those which have been describedhereabove.

13. Sigh On/Off

A sigh on/off button 360 is provided. When sigh on/off button 360 isdepressed, the controller 12 will cause the ventilator 14 to deliver asigh breath. A sigh breath is a volume-controlled, mandatory breath thatis usually equal to 1.5 times the current tidal volume setting shown ontidal volume setting display 332. The sigh breath is delivered accordingto the current peak flow setting shown on peak flow setting display 336.The inspiratory phase of the sigh breath is preferably limited to amaximum of 5.5 seconds. During a sigh breath, the breath period isautomatically increased by a factor of 1.5. The sigh breath function isavailable during all ventilation modes.

A single depression of the sigh on/off button 348 will cause theventilator to deliver a volume-controlled sigh breath once every 100breaths or every 7 minutes, which ever comes first. The sigh breathbutton 360 includes a visual indicator light 360a which illuminates whenthe sigh on/off button 360 is depressed and the sigh/breath function isactive.

14. Manual Breath

A manual breath button 362 is also provided. Upon depression of themanual breath button 362, the controller 12 will cause the ventilator 14to deliver a single volume-controlled or pressure-control breath inaccordance with the associated volume and/or pressure control settings.An indicator light 362a will illuminate briefly when manual breathbutton 362 is depressed.

15. Remote Alarm (Optional)

A remote alarm on/off control button 364 is provided to enable ordisable the remote alarm. When the remote alarm on/off control button364 is depressed, indicator light 364a will illuminate. When the remotealarm on/off button 364 is depressed, the remote alarm will be enabled.When this function is enabled, alarm conditions will transmit via hardwire or radio frequency (wireless) to a remote alarm which may bemounted on the outside of a patients room so as to signal attendantsoutside of the room, when an alarm condition exists.

The specific alarm conditions which may be utilized with the remotealarm function, are described in greater detail herebelow.

16. Flow Waveform (Optional--Applies To Volume Breaths Only)

The controller 12 includes a square flow wave form activation button 366and a decelerating taper flow wave form actuation button 368. When thesquare flow wave form actuation button 366 is depressed, indicator light366a will illuminate, and the ventilator will deliver inspiratory flowat a constant rate according to the peak flow setting, as input andshown on peak flow display 336. When the decelerating paper wave formactuation button 368 is depressed, indicator light 368a will illuminate,and the ventilator will deliver an inspiratory flow which initiallyincreases to the peak flow setting, as input and shown on peak flowdisplay 336, then such inspiratory flow will decelerate to 50 percent ofthe peak flow setting at the end of the inspiratory phase.

17. Inspiratory Hold (Optional)

An inspiratory hold actuation button 370 is provided, to enable theoperator to hold the patient at an elevated pressure followinginspiration, so that breath mechanics can be calculated. The length ofthe delay period is determined by the period of time during which theinspiratory hold button 370 remains depressed, with a maximum limitapplied.

18. Expiratory Hold (Optional)

The controller 12 also includes expiratory hold actuation button 372,which enables the ventilator to calculate auto PEEP. During theexpiratory hold, the turbine 30 operation is halted and the exhalationvalve 18 remains closed. The difference between the end expiratorypressure, as measured at the end of the expiratory hold period, minusthe airway pressure reading recorded at the beginning of the expiratoryhold period, will be displayed on monitor window 384.

19. Maximal Inspiratory Pressure/Negative Inspiration Force (Optional)

The preferred controller 12 also incorporates a maximal inspiratorypressure test button 374, to enable the operator to initiate a maximalinspiratory pressure (MIP) test maneuver. This maneuver causes theventilator to stop all flow to or from the patient. The patientinspiratory effort is then monitored and displayed as MIP/NIF in themonitor window 384.

20. 100% O₂ Suction (Optional)

Optionally, the controller 12a includes a 100% O₂ actuation button 376which, when depressed, will cause indicator light 376a to illuminate andwill cause the system 10 to deliver an FiO₂ of 1.00 (i.e., 100% oxygen)to the patient for a period of three (3) minutes regardless of thecurrent FiO₂ setting and/or breath type setting.

This 100% O₂ feature enables the operator to selectively deliver 100%oxygen to the patient PT for a three minute period to hyperoxygenate thepatient PT prior to disconnection of the patient from the ventilatorcircuit for purposes of suctioning, or for other clinical reasons.

21. Additional Control Actuation Buttons

An additional control actuation button 378, with indicator light 378a,is provided to enable the controller 12a to be subsequently programmedto perform additional control actuation functions beyond those describedhereabove.

MONITORS AND INDICATORS

1. AC Power Status Indicator

An AC power indicator light 304 is provided in the face panel of thecontroller 12 to indicate when sufficient AC power is available and thestandby/off switch (not shown) is in the standby position.

2. Internal Battery Status Indicator(s)

An internal battery status indicator light 308 is provided on the panelof the controller 12, and will indicate battery charge level accordingto predetermined color signals. A separate internal battery chargeindicator light 306 may be provided, and will indicate charging statusaccording to predetermined color signals.

3. External Battery Status Indicator(s)

An external battery status indicator light 312 is provided on the panelof the controller 12, and will indicate battery charge level accordingto predetermined color signals. A separate external battery chargeindicator light 310 may be provided, and will indicate charging statusaccording to predetermined color signals.

4. Airway Pressure Monitor

The display panel of the controller 12 includes a real time airwaypressure bar graph display 380. A green indicator bar will appear on theairway pressure bar graph display 380 to indicate the real time airwaypressure at all times. Red indicators will appear on the airway pressurebar graph to indicate high and low peak pressure alarm setting, as morefully described herebelow under the heading "Alarms". An amber coloredindicator will appear on the airway pressure bar graph display 380 toindicate the current PEEP/CPAP setting, Pressure Support setting and/orPressure Control setting. A patient effort indicator light 382 islocated near the airway pressure bar graph display 380, and willilluminate to indicate the occurrence of a patient-initiated breath,including all spontaneous, assist or pressure support breaths.

5. Digital Monitor Display

The panel of the controller 12 preferably includes a digital monitordisplay 384 and an accompanying monitor select button 386. Thecontroller 12 is programmed to display various monitored parameters.Each time the monitor select button 386 is depressed, the monitoredparameters displayed on monitor display 384 will change. The individualparameters may include: exhaled tidal volume, i.e., ratio, mean airwaypressure, PEEP, peak inspiratory pressure, total breath rate, totalminute ventilation.

Additionally, a display power saving feature may be incorporated,whereby the controller 12 will automatically cause the monitor display384 to become non-illuminated after a predetermined display period whenthe system 10 is operating solely on internal or external battery power.Each time the monitor select button 386 is depressed, the display 384will illuminate for a predetermined period of time only, and then wallbecome non-illuminated. This feature will enable the system 10 toconserve power when the system 10 is being operated solely on internalor external battery power.

Additionally, the controller 12 may be programmed to cause the monitordisplay 384 to display a special or different group of parameters duringa specific operator-initiated maneuver. Examples of special parametergroups which may be displayed during a specific maneuver include thefollowing:

Real-time Pressure (at start of and during all maneuvers)

Plateau Pressure (Inspiratory Hold)

Compliance (Inspiratory Hold)

End Expiratory Pressure (Expiratory Hold)

Auto PEEP (Expiratory Hold)

Maximal Inspiratory Pressure (MIP/NIF)

Alarms And Limits

The preferred controller 12 may be programmed to received operator inputof one or more limiting parameters, and to provide audible and/or visualalarm indications when such limiting parameters have been, or are aboutto be, exceeded.

The visual alarm indicators may comprise steady and or flashing lightswhich appear on the control panel of the preferred controller 12a.

The audible alarm components will preferably comprise electronic buzzersor beepers which will emit sound discernable by the human ear for apreselected period (e.g., 3 seconds). Preferably, the audible portion ofany alarm may be volitionally muted or deactuated by the operator.

Additionally it is preferable that the controller 12 be programmed toautomatically reset each alarm if the current ventilation conditions donot fall outside of the preset alarm limits.

Examples of specific limiting parameters and alarm limits which may beprogrammed into the preferred controller 12, are as follows:

1. High Peak Pressure

The preferred controller 12 includes, on its face panel, a high pressuredigital display 390 and a corresponding high pressure alarm limitsetting button 390a. When the high pressure alarm limit setting button390a is depressed, value setting knob 300 may be utilized to dial in adesired high pressure alarm limit value. Such high pressure alarm limitvalue will then be displayed on high pressure alarm limit display 390.

The currently set high pressure alarm limit, as shown on high pressurealarm limit display 390, will establish the maximum peak inspiratorypressure for all breath types. When the monitored airway pressureexceeds the currently set high pressure alarm limit, audible and visualalarms will be actuated by the controller 12 and the controller willimmediately cause the system 10 to cycle to expiratory mode, therebyallowing the airway pressure to return to the baseline bias flow leveland along the exhalation valve 18 to regulate pressure at anycurrently-set peep level.

In order to avoid triggering of the high pressure alarm during deliveryof a sigh breath, the controller 12 will be programmed to automaticallyadjust the high pressure alarm limit value by a factor of 1.5× duringthe delivery of a sigh breath, provided that such does not result in thehigh pressure limit value exceeding 140 cmH₂ O. The controller 12 ispreferably programmed not to exceed a high pressure limit setting of 140cmH₂ O, even during delivery of a sigh breath.

2. Low Peak Pressure

A low peak airway pressure limit display 392, and corresponding low peakpressure limit setting button 392a, are also provided. When the low peakpressure limit setting button 392a is depressed, value setting knob 300may be utilized to dial in a desired low peak airway pressure alarmlimit value. Such low peak pressure alarm limit value will then bedisplayed in the low peak pressure display 392.

Audible and/or visual alarms will be activated if the monitored airwaypressure fails to exceed the low peak pressure alarm limit settingduring the inspiratory phase of a machine-cycled mandatory or assistbreath.

The controller 12 is preferably preprogrammed to deactivate the low peakairway pressure alarm during spontaneous, CPAP and pressure supportbreathing.

The range of low peak pressure settings will preferably be from 2 to 140cmH₂ O.

3. Low Minute Volume

A low minute volume display 394, and corresponding low minute volumesetting button 394a are provided. When low minute volume setting button394a is depressed, value setting knob 300 may be used to dial in thedesired low minute volume alarm setting. The currently-set low minutevolume alarm setting will be displayed in digital display 394.

The controller 12 will be programmed to calculate the current exhaledminute volume based or information received from the exhalation valvedifferential pressure transducer 70, and to trigger audible and/orvisual alarms when the exhaled minute volume becomes less than or equalto the currently set low minute volume alarm limit. This alarm is activefor all breath types.

The typical range of setable low minute volume alarm limits is from 0 to99.9 liters/min.

4. Apnea Alarm

The controller 12 may be programmed to trigger auditory and/or visualapnea alarms when the period between initiation of inspiratory phasesexceeds 20 seconds. The controller 12 is preferably also programmed toinitiate back-up machine ventilation when an apnea alarm conditionexists.

The controller 12 is preferably programmed not to permit volitionalsilencing of the apnea alarm until the apnea condition has beencorrected.

5. Spare Alarm Limit Displays And Setting Buttons

Spare alarm limit displays 396, 398, and corresponding spare alarm limitsetting buttons 396a and 398a are provided, to permit the controller 12to be subsequently expanded or programmed to receive operator input ofadditional limiting parameters, and to provide auditory and/or visualalarms when such limiting parameters have been exceeded.

6. Ventilator Inoperative

A separate ventilator inoperative light indicator 400 is provided on theface panel of the controller 12. The controller 12 is programmed tocause the ventilator inoperative light to illuminate when predetermined"ventilatory inoperative" conditions exist.

7. AC Power Low/Fail

The controller 12 is preferably programmed to activate visual and/orauditory alarms when an AC power cord is connected to the system 10 andthe voltage received by the system 10 is outside of a specifiedoperating range. The controller 12 is preferably also programmed toautomatically switch the system 10 to internal battery power under thiscondition. The AC power low/fail alarm can be silenced, and will remainsilenced, until such time as the internal low battery alarm 208 becomesactuated, indicating that the internal battery has become depleted.

8. External/Internal Battery Low/Fail

The controller 12 may be programmed to actuate a visual and or auditoryalarm when an external or internal battery is in use, and the batteryvoltage is outside of an acceptable operating range.

9. O₂ Inlet Pressure

The controller 12 may be programmed to provide auditory and/or visualalarms when the oxygen pressure delivered to the system 10 is above orbelow predetermined limits.

10. Over Pressure Relief Limit

The system 10 includes a mechanical variable pressure relief valve 64,to relieve any over pressurization of the patient circuit.

The range of setable over pressure relief limit values may be between 0to 140 cmH₂ O.

SELF TESTING AND AUTO CALIBRATION FUNCTIONS

1. Self Test Function

The preferred controller 12 may be programmed to perform a self-testingfunction each time the ventilator is powered up. Such self testingfunction will preferably verify proper functioning of internalcomponents such as microprocessors, memory, transducers and pneumaticcontrol circuits. Such self testing function will also preferably verifythat electronic sub-systems are functioning correctly, and are capableof detecting error conditions relating to microprocessor electronics.

Also, during power up, the controller 12 may be programmed to allow aqualified operator who enters a given key sequence, to access troubleshooting and calibration information. In accordance with this feature,the key operator may induce the controller to display, on the monitordisplay 384, information such as the following:

SOFTWARE REVISION

PEAK FLOW AND PRESSURE TRANSDUCER OUTPUT

LAMP TEST/ALL DISPLAYS ON ANY AUTO ZERO AND PURGE FUNCTIONS FOR THE FLOWPRESSURE TRANSDUCER

EVENT DETECTION MENU INCLUDING PREVIOUS STATUS OR FAULT CODES

REMOTE ALARM TEST AND PROGRAM; and

DATA COMMUNICATIONS TEST AND PROGRAM

Also, the controller 12 may be programmed to allow a qualified operatorwho entered a given key sequence, to access a user preference and set upmenu. Such menu may include a monitory display 384, of information suchas the following:

System lock, enable or disable;

Variable Apnea interval;

Language selection; and

User verification tests.

The user preference and set up menu function may also be accessibleduring operation of the system 10.

C. A Preferred Rotary Drag Compressor Apparatus

The portable system 10 ventilator of the present invention preferablyincorporates a rotary drag compressor apparatus 30 comprising adual-sided, multi-bladed rotor 104 disposed within a rigid compressorhousing 106. An inflow/outflow manifold 108 is formed integrally withthe compressor housing 106, and incorporates two (2) inflow passageways112 and two (2) outflow passageways 110 for channeling gas flow into andout of the compressor apparatus 30.

An electric motor 102, such as a 0.8 peak horsepower, 40 volt D.C.motor, is preferably mounted integrally within the compressor housing106. Alternatively, the motor 102 may be encased or housed in anencasement or housing which is separate from the compressor housing 106.The motor shaft 114 extends transversely into a bore 116 formed in thecentral hub 118 of rotor 104. As shown, the bore 116 of the central hub118 of rotor 104 may include a rectangular key-way 121 formed on oneside thereof and the motor shaft 114 may include a correspondingelongate rectangular lug formed thereon. The rectangular lug of themotor shaft 114 inserts within and frictionally engages the key-way 121of the rotor hub 118, thereby preventing the motor shaft 114 fromrotationally slipping or turning within the bore 116 of the rotor hub118. It will be appreciated however, that various alternative mountingstructures, other than the lug and keyway 121 shown in FIGS. 8-9, may beutilized to rotatably mount the motor shaft 114 to the rotor 104.

The rotor hub 118 is preferably formed having a concave configuration,as shown in FIG. 5. Such concave configuration serves to impartstructural integrity and strength to the rotor 104, withoutsignificantly increasing the mass of the rotor 104 as would result fromthe formation of additional strengthening ribs or bosses on the rotorhub 118.

As shown in FIGS. 5-10, a first annular trough 120 extends about theperiphery of the front side of the rotor 104, and a second annulartrough 122 extends about the periphery of the backside of the rotor 104.

A multiplicity of rotor blade-receiving slots 126 are formed angularly,at evenly spaced intervals about the inner surfaces of the first 120 andsecond 122 annular troughs. Rotor blades 128 are mounted at spaced-apartlocations around each annular trough 120, 122 such that the radialperipheral edge 127 of each blade 128 is inserted into and resideswithin a corresponding blade receiving slot 126 and the leading edge 129of each blade traverses across the open annular trough 120 or 122, asshown. Each blade 128 is affixed by adhesive, or other suitable means,to the body of the rotor 104.

In the preferred embodiment the blades 128 are located in axiallyaligned positions, i.e., non-staggered directly opposite positions onopposite sides of the rotor 104 so as to promote even pressure balanceand symmetrical weight distribution within the rotor 104.

The rotor 104 is rotatably mounted within the compressor housing 106such that the first 120 and second 122 annular cavities are in alignmentwith the inflow 110 and outflow 112 channels, as shown.

In order to optimize the controllability of the rotor 104 velocity, andto minimize the wear or stress on the system drive components fromrepeated abrupt starting and stopping of the rotor 104, it is desirablethat the overall mass of the rotor 104 be minimized. Toward this end,the body of the rotor 104 is preferably constructed of light weightmaterial such as aluminum, and the individual blades 128 of the rotor104 are preferably constructed of light weight material such asglass-filled epoxy. In embodiments where the body of the rotor 104 isformed of aluminum and the blades 128 are formed of glass-filled epoxy,a suitable adhesive such as epoxy may be utilized to bond the radialedges of the blades 128 within their corresponding blade-receiving slots126. Alternatively, it is contemplated to form the rotor and bladesintegrally, as by way of a molding process whereby metal (e.g.,aluminum), polymer or composite materials are molded to form the blades128 and rotor 104 as a unitary structure.

After the rotor blades 128 have been mounted and secured in theirrespective blade-receiving slots 126, each individual blade 128 willpreferably be disposed at an angle of attack A, relative to a flattransverse plane TP projected transversely through the body of the rotor104, between the first annular trough 120 on the front side of the rotor104, and the second annular trough 122 on the backside of the rotor 104.The angle A is preferably in the range of 30-60 degrees and, in thepreferred embodiment shown in FIGS. 8-10 is 55 degrees. Such angle A isselected to provide optimal flow-generating efficiency of the rotor 104.

In operation, it is necessary to precisely control the timing of theacceleration, deceleration, and the rotational speed, of the rotor 104in order to generate a prescribed inspiratory pressure and/or flow rateand/or volume. Although standard manufacturing tolerances may bemaintained when manufacturing the rotor 104 and other components of thecompressor 30 (e.g., the rotor 104, compressor housing 106, motor 102)each individual compressor 30 will typically exhibit some individualvariation of flow output as a function of the rotational speed anddifferential pressure of that compressor 30. Thus, in order to optimizethe precision with which the inspiratory flow may be controlled, it isdesirable to obtain precise flow and pressure data at various turbinespeeds for each individual compressor 30, and to provide suchcharacterization data to the controller 12 to enable the controller 12to adjust for individual variations in the pressure and/or flow createdby the particular compressor 30 in use. As a practical matter, this maybe accomplished in either of two ways. One way is to generate discreteflow rate, speed and pressure measurements for each compressor 30 at thetime of manufacture, and to provide a table of such discreet flow rate,speed and pressure values to the ventilator controller 12 at the timethe particular compressor 30 is installed. The controller 12 will becorrespondingly programmed to perform the necessary interpolativemathematical steps to obtain instantaneous flow, speed or pressuredeterminations as a function of any two such variables, for theparticular compressor 30. The second way is to experimentally generate aseries of flow, speed and pressure data points over a range of normaloperating rotor speeds, and to subsequently derive a unique speed vs.flow vs. pressure equation to characterize each individual compressor30. Such individual characterization equation is then programmed into,or otherwise provided to, the controller 12 and the controller 12 isprogrammed to utilize such equation to compute precise, instantaneousspeed, flow rate and pressure control signals for controlling theindividual compressor 30 in use. An example of such graphical speed vs.flow rate vs. pressure data, and a characterization equation derivedtherefrom, is shown in FIG. 12.

Given the current cost of microprocessor technology, providing acontroller 12 which has the capability to receive and process such acharacterization equation as shown in (FIG. 12) for controlling thecompressor 30 would require substantial expense and size enlargement ofthe controller 12. Accordingly, given the present state of the art, itis most desirable to utilize the former of the two above-describedmethods--that is, providing a database of discrete flow, speed andpressure values and programming of the controller 12 to perform thenecessary mathematical interpolations of the provided data points formaintaining compressor-specific control of the pressure, flow rateand/or volume of gas provided in each inspiratory phase at theventilation cycle. The experimentally generated database of discreetflow, speed and pressure valves may be encoded onto an EPROM or anyother suitable database storage device. Such EPROM or other databasestorage device may be located on or within the compressor 30 itself andcommunicated to the controller 12 via appropriate circuitry.Alternatively, such EPROM or database storage device may be installeddirectly into the controller 12 at the time the particular compressor 30is installed within the ventilator device 14.

The controlled inspiratory flow generated by the rotary drag compressor30, exists from the compressor outlet 34 and through line 22 to thepatient PT. As shown in FIG. 2, an output silencer 60, such as a hollowchamber having a quantity of muffling material formed therearound, ispreferably positioned on inspiratory flow line 22 to reduce the soundgenerated by the ventilator 14 during operation. An inspirationocclusion valve 62 is additionally preferably mounted on inspiratoryflow line 22 to accomplish operator controlled stoppage of theinspiratory flow as required during performance of a maximal inspiratoryforce maneuver. Additionally, a pressure relief valve 64 is connected toinspiratory flow line 22 to provide a safeguard against deliveringexcessive inspiratory pressure to the patient PT. The pressure reliefvalve 64 may be manually set to the desired limit pressure, by theoperator.

In general, the rotary drag compressor ventilator 14 operates byperiodic rotating of the rotor 130 within the compressor 30 to generatethe desired inspiratory gas flow through line 22. It is desirable thatthe rotor 130 be accelerated and decelerated as rapidly as possible.Such rapid acceleration/deceleration is facilitated by a reduction ininertial effects as a result of the above-described low massconstruction of the rotor 104. The speed and time of rotation of therotor 104, during each inspiratory phase of the ventilator cycle, iscontrolled by the controller 12 based on the variables and/or parameterswhich have been selected for triggering, limiting and terminating theinspiratory phase.

The precise flow, volume or pressure delivered through the inspiratoryline 22 is controlled by the controller based on the EPROM-storedcompressor characterization data received by the controller, as well asperiodic or continuous monitoring of the rotational speed of the rotor104 and the change in pressure (Δ_(p)) between the inlet side 32 andoutlet side 34 of the compressor 30 as monitored by the differentialpressure transducer 36.

In the presently preferred embodiment, the controller 12 is programmedto deliver breaths by either of two available closed loop algorithms;volume or pressure.

Example: Volume Breaths

Prior to Volume breath initiation, the controller 12 generates apredefined command waveform of flow vs time. The waveform is generatedusing the current Flow, Volume and Waveform input settings from thefront panel. Since the mathematical integral of flow over time is equalto the volume delivered, the controller can determine the appropriateinspiratory time. Once a volume breath has been triggered, thecontroller uses closed loop control techniques well known in the art todrive the compressor, periodically read the compressor differentialpressure and rotational speed, and then calls upon the specific storedcompressor characterization data to arrive at the actual flow rate. Onceactual flow rate is known, it is compared or "fed back" to the currentcommanded flow, and a resulting error is derived. The error is thenprocessed through a control algorithm, and the compressor speed isadjusted accordingly to deliver the desired flow rate. This process isrepeated continuously until the inspiration is complete.

Example: Pressure Breaths

Pressure breaths include several breath types such as Pressure Supportor Pressure Control. In these breath types, the controller commands thecompressor to provide flow as required to achieve a pressure as inputfrom the front panel. Once a pressure breath has been triggered, thecontroller uses closed loop control techniques well known in the art todrive the compressor 30 and to achieve the desired patient airwaypressure. The controller periodically reads the actual airway pressure.Once actual pressure is known, it is "fed back" and compared to thecurrent commanded pressure, and a resulting error is derived. The erroris then processed through a control algorithm, and the compressor speedis adjusted accordingly to deliver the desired pressure. This process isrepeated continuously until the inspiration is complete.

For both breath types, once the selected inspiratory terminationvariable is reached, the controller will signal the compressor motor 102to stop or decelerate to a baseline level, thereby cycling theventilator in to the expiratory phase.

D. A Preferred Oxygen Blending Apparatus

When oxygen enrichment of the inspiratory flow is desired, thecontroller 12 may be additionally programmed or equipped to control theoperation of the oxygen blending apparatus 16 to mix a prescribed amountof oxygen with ambient air drawn through air intake 24, therebyproviding an inspiratory flow having a prescribed oxygen content (FiO₂)between 21%-100%.

As shown in FIGS. 2 and 3, the preferred oxygen blending apparatus 16comprises an air inlet line 24 which opens into a hollow vessel oraccumulator 54.

Oxygen inlet line 26 is connected to a pressurized source of oxygen andleads, via a manifold to a series of solenoid valves 52. Although not byway of limitation, in the preferred embodiment as shown in FIG. 3, five(5) separate solenoid valves 52a-52e are utilized. Each such separatesolenoid valve 52a-52e has a specific (usually differing) sized flowrestricting orifice formed therein so that each such solenoid valve52a-52e will permit differing amounts of oxygen to pass into accumulator54, per unit of time during which each such solenoid valve 52a-52e ismaintained in an open position. The controller 12 is preprogrammed todetermine the specific period(s) of time each solenoid valve 52a-52emust remain open to provide the necessary amount of oxygen toaccumulator 54 to result in the prescribed oxygen concentration (FiO₂).

Algorithm for a Preferred Oxygen Blending Apparatus

The rotational velocity of the rotor 104 and differential pressureacross the inflow/outflow manifold 108 are measured by the controller 12and from this data the controller 12 is able to determine the flow ofgas through the compressor 30 from the accumulator 54. The controller 12integrates the air flow drawn through the compressor 30 to determine theaccumulated volume of enriched gas drawn from said accumulator 54. Inorder to maintain the flow of gas at the prescribed FiO₂ level, aportion of this removed volume must be replaced in the accumulator 54with pure oxygen.

The accumulated volume is compared to a predetermined trigger volume foreach of the solenoids 52a-52e, which in the preferred embodiment, isdefined by the equation:

    Trigger Volume=(Solenoid Flow*Time*79)/ (FiO.sub.2 -21)*2!

Starting with the smallest, each solenoid that is not currently open iscompared. When the accumulated volume reaches the trigger volume for asolenoid 52, the controller 12 opens that solenoid 52 for a period oftime allowing oxygen to flow from the oxygen inlet line 26 through thesolenoid 52 and into the accumulator 54. The controller 12 then adjuststhe accumulated volume appropriately by subtracting a volume,proportional to the volume of oxygen delivered to the accumulator 54from the accumulated volume defined by the equation:

    Subtracted Volume=(Solenoid Flow*Time*79)/(FiO.sub.2 -21).

This process is repeated continuously.

The trigger volume the controller 12 uses to open an individual solenoid52a-52e is independent for each solenoid 52 and is function of the flowcapacity of the particular solenoid 52a-52e, the prescribed FiO₂ level,and the amount of time the solenoid 52 is open. In the preferredembodiment, the amount of time each solenoid 52 is open is the same foreach solenoid 52, but may vary as a function of oxygen inlet pressure.

Example: Delivery of 0.6 FiO₂ Using 4 Solenoids

In this example, the oxygen blending apparatus has 4 solenoids withflows of 5 lpm, 15 lpm, 40 lpm, and 80 lpm respectively. The FiO₂setting is 60%, thus the trigger volumes for each of the 4 solenoids is8 ml, 25 ml, 66 ml, and 133 ml respectively. Furthermore a constantoxygen inlet pressure is assumed resulting in an "on" time of 100 ms forthe solenoids, a constant compressor flow of 60 lpm, and a period of 1ms. The following table describes the state of the oxygen blendingalgorithm after various iterations:

    ______________________________________         Accumulated                   Solenoid Solenoid                                    Solenoid                                           Solenoid    Time Volume    1        2       3      4    (ms) (ml)      (8 ml)   (25 ml) (66 ml)                                           (133 ml)    ______________________________________    0    0         off      off     off    off    1    1         off      off     off    off    2    2         off      off     off    off    **    7    7         off      off     off    off    8    0         on       off     off    off    9    1         on       off     off    off    **    32   24        off      off     off    off    33   0         on       on      off    off    34   1         on       on      off    off    **    98   65        on       on      off    off    99   0         on       on      on     off    100  1         on       on      on     off    **    107  8         on       on      on     off    108  1         off > on*                            on      on     off    ______________________________________     *At 108 ms the 8 ml solenoid turned off after having been on for 100 ms,     but since the accumulated volume is now 9 ml the solenoid is turned on     again.

Thus, by independently operating the four (4) separate solenoids asshown in the above table, a 0.6 FiO₂ is consistently delivered throughthe compressor 30.

E. A Preferred Exhalation Valve and Exhalation Flow Transducer

Referring generally to FIGS. 11a-11e the preferred exhalation valve andexhalation flow transducer assembly of the present invention isdepicted. By way of overview, the exhalation valve 18 comprises ahousing which defines an expiratory flow path therethrough and a valvingsystem for controlling the airway pressure during the expiratory phaseof the ventilation cycle. The exhalation valve 18 shares numerousstructural and functional attributes with the exhalation valve describedin U.S. Pat. No. 5,127,400 (DeVries et al) entitled VentilatorExhalation Valve, issued Jul. 7, 1994, the disclosure of which isexpressly incorporated herein by reference.

In addition, the exhalation valve assembly 18 of the present inventionadditionally incorporates an exhalation flow transducer 230 which servesto monitor exhalation flow from the patient and generates an outputsignal to the controller 12. The output signal is then utilized by thecontroller to determine when patient exhalation has ceased to therebyinitiate inspiratory flow to the patient. In the preferred embodiment,the exhalation flow transducer 230 is mounted within the exhalationvalve 18 in unique structure to minimize manufacturing inaccuracies.Further, in the preferred embodiment, the particular operationalcharacteristics of the exhalation flow transducer 230 are stored withina memory device which is then communicated to the controller 12 toinsure accuracy in flow measurements. The exhalation flow transducer 230of the present invention shares numerous structural and functionalattributes with the flow transducer described in the U.S. Pat. No.4,993,269, issued to Guillaume et al., entitled Variable Orifice FlowSensing Apparatus, issued on Feb. 19, 1991, the disclosure of which isexpressly incorporated herein by reference.

Referring more particularly to FIGS. 11a through 11e, the exhalationvalve 18 of the present invention is formed having a housing 200including an exhalation tubing connector 202 formed at a first locationthereon and an outflow port 204 formed at a second location thereon. Anexhalation gas flow passageway 206 extends through the interior of thehousing 200 such that expiratory gas may flow from the exhalation tubingconnector 202 through the exhalation passageway 206 within the interiorof the exhalation valve 18 and subsequently passed out of the outflowport 204. Midway through the expiratory flow passageway 206, there isformed an annular valve seat 208. The annular valve seat 208 may bedisposed in a plane which is parallel to the plane of the flat diaphragm210 or alternatively, as in the embodiment shown, the annular valve seat208 may be slightly angled or tapered relative to the plane in which theflat diaphragm 210 is positioned. Such angling or tapering of the valveseat 208 facilitates seating of the diaphragm 210 on the valve seat 208without flutter or bouncing of the diaphragm 210. The elastomeric discor diaphragm 210 is configured and constructed to initially contact thefarthest extending side of the angled valve seat 208, and tosubsequently settle or conform onto the remainder of the angled valveseat 208, thereby avoiding the potential for flutter or bouncing whichmay occur when the diaphragm 210 seats against a flat non-angled valveseat 208.

The disc or diaphragm 210 is preferably attached to the surroundingrigid housing 200 by way of an annular flexible frenulum 212. Frenulum212 serves to hold the disc or diaphragm 210 in axial alignment with theannular valve seat 208, while permitting the disc or diaphragm 210 toalternatively move back and forth between a closed position wherein thediaphragm 210 is firmly seated against the valve seat 208 (FIG. 11a) anda fully open position wherein the disc or diaphragm 210 is retractedrearwardly into the adjacent cavity within the housing 200 therebyproviding an unrestricted flow path 206 through which expiratory gas mayflow.

A pressure distributing plate 214 is mounted on the backside of thediaphragm 210. A hollow actuation shaft 216 is mounted within thehousing 200 and is axially reciprocal back and forth to control theposition of the diaphragm 210 relative the valve seat 208. A bulbous tipmember 218 is mounted on the distal end of a hollow actuation shaft 216.A corresponding pressure distribution plate 214 is mounted on the backof the diaphragm 210. Forward movement of the actuation shaft 216 causesthe bulbous tip member 218 to exert forward pressure against the plate214 thereby forcing the diaphragm 210 toward its closed position. Whenthe actuation shaft 216 is in a fully forward position, the diaphragm210 will be held in firm abutment against the annular valve seat 208thereby terminating flow through the passage 206. Conversely when theactuation shaft 216 is retracted, the diaphragm 210 moves away from thevalve seat 208 thereby allowing flow through the passageway 206 therebyallowing flow through the passageway 206.

The movement of the shaft 216 is controlled by way of an electricalinduction coil 220 and spider bobbin 222 arrangement. In the preferredembodiment, the electrical induction coil 220 is formed without havingan internal support structure typically utilized in induction coils soas to minimize inertial concerns. In this regard, the coil 220 istypically formed by winding upon a mandrel and subsequently maintainedin this wound configuration by way of application of a suitable binderor varnish. Additionally, in the preferred embodiment, the bobbin 222 ispreferably formed having a cross-beam construction, as shown in FIG.11b, to decrease the mass of the bobbin 222 while maintaining itsstructural integrity. Similarly, the shaft 216 is preferably formed froma hollow stainless steel material so as to be relatively strong yetlight weight enough for minimizing inertial concerns.

As shown, the bobbin 222 is affixed to the distal end of the inductioncoil 220 and the shaft 216 extends through an aperture formed in thecenter of the bobbin and is frictionally or otherwise affixed to thebobbin such that the shaft 216 will move back and forth in accordancewith the bobbin 222 and coil 220. As the current passing into theinduction coil 220 increases, the coil 220 will translate rearwardlyinto the coil receiving space 226 about the magnet thereby moving theshaft 216 and blunt tip member 218 in the rearward direction andallowing the diaphragm 210 to move in an open position away from thevalve seat 208 of the expiratory flow path 206. With the diaphragm 210in such open position, expiratory flow from the patient PT may passthrough the expiratory flow pathway 206 and out the expiratory port 204.

Conversely, when the expiratory flow has decreased or terminated, thecurrent into the induction coil may change direction, thereby causingthe induction coil to translate forwardly. Such forward translation ofthe induction coil 220 will drive the bobbin 222, shaft 216, and bulboustip member 218 in a forward direction, such that the bulbous tip member218 will press against the flow distributing plate 214 on the backsideof the diaphragm 210 causing the diaphragm to seat against the valveseat 208. With the diaphragm 210 seated against the valve seat 208, theinspiratory phase of the ventilator cycle may begin and ambient air willbe prevented from aspirating or backflowing into the patient circuitthrough the exhalation port 204.

In the preferred embodiment, a elastomeric boot 217 or dust barrier ismounted about the distal portion of the hollow actuation shaft 216, andis configured and constructed to permit the shaft 216 to freely moveback and forth between its fully extended closed position and a fullyretracted open position while preventing dust or moisture from seepingor passing into the induction coil 220.

As best shown in FIG. 11, FIGS. 11a and 11c, the housing of theexhalation valve 18 includes a frontal portion formed by the housingsegments 200b, 200c, and 200d. An airway pressure passage 241 isprovided within the housing portion 200b, which enables the pressurewithin the exhalation passageway 206 to be communicated to an airwaypressure tubing connector 233. Airway pressure tubing connector 233 isconnected via tubing to an airway pressure transducer 68 (shown in FIG.2) which monitors airway pressure and outputs a signal to the controller12. Based upon desired operating conditions, the controller 12, inresponse of receipt of the pressure signal from pressure transducer 68increases or decreases the voltage applied to the coil 220 to maintaindesired pressure within the exhalation air passage 206. As will berecognized, such monitoring of the airway pressure is continuous duringoperation of the ventilator cycle.

As previously mentioned, the exhalation flow transducer 230 of thepresent invention is preferably disposed with the exhalation valvehousing and serves to monitor exhalation flow from the patient PT. Moreparticular, the exhalation flow transducer 230 of the present inventionpreferably incorporates a feedback control system for providing realtime monitoring of the patient's actual expiratory flow rate. As bestshown in FIGS. 11a and 11c, the expiratory flow transducer 230 of thepresent invention is incorporated within the exhalation flow path 206within housing segment 200b. The flow transducer 230 is preferablyformed from a flat sheet of flexible material having a cut out region406 formed therein. A peripheral portion 408 of the flat sheet existsoutside of the cut out region 406 and flapper portion 231 is definedwithin the cut out region 406. Frame members 410 and 412 preferablyformed of a polymer material, are mounted on opposite sides of the flatsheet so as to exert inward clamping pressure on the peripheral portion408 of the flat sheet. The flapper portion 231 of the flat sheet is thusheld in its desired transverse position within the open central aperture14a and 14b of the transducer assembly, and such flapper portion 231 isthus capable of flexing downstream in response to exhalation flow.

To minimize the inducement of stresses within the flow transducerassembly 230, a frame member 411 is preferably positioned in abuttingjuxtaposition to the outboard surface of at least one of the framemembers 410, 412. In the preferred embodiment shown in FIG. 11c, theframe member 411 is positioned in abutment with the upper frame member410. Such frame member 411 comprises a metal frame portion 413 andincludes an elastomeric cushioning gasket or washer 415 disposed on thelower side thereof. A central aperture 14c is formed in the frame member411, such aperture 14c being of the same configuration, and in axialalignment with central apertures 14a, 14b of the upper and lower framemembers 410, 412.

Upper and lower abutment shoulders 418a, 418b, are formed within theexhalation valve housing 200 to frictionally engage and hold the flowtransducer assembly 230 in its desired operative position. When soinserted, the upper engagement shoulder 418a will abut against the uppersurface of the frame member 411, and the lower abutment shoulder 418bwill abut against the lower surface of the lower frame member 412,thereby exerting the desired inward compressive force on the flowtransducer assembly 230. As will be recognized, the inclusion of thecushioning washer 415 serves to evenly distribute clamping pressureabout the peripheral portion 408, thereby minimizing the creation oflocalized stress within the flow transducer 230.

When the transducer assembly 230 is operatively positioned between theupper and lower abutment shoulders 418a, 418b, an upstream pressure port232 will be located upstream of the flapper 231, and a downstreampressure port 234 will be located downstream of the flapper 231. By sucharrangement, pressures may be concurrently measured through upstreampressure port 232 and downstream pressure port 234 to determine thedifference in pressures upstream and downstream of the flapper 231.

As expiratory gas flow passes outwardly, through the outlet port of theexhalation valve 18, the flapper portion 231 of the flow transducer 230will deflect or move allowing such expiratory gas flow to passthereacross, but also creating a moderate flow restriction. The flowrestriction created by the flow transducer 230 results in a pressuredifferential being developed across the flow transducer 230. Suchpressure differential may be monitored by pressure ports 232 and 234disposed on opposite side of the flow transducer 230 (as shown in FIG.11a) which pressure ports are in flow communication by internal passagesformed within the housing segment 200c, 200b and 200a to tubingconnections 240 and 235. A manifold insert 201 may be mounted on theupstream pressure port 232 such that the manifold insert 201 protrudesinto expiratory flowpath 206, upstream of the flapper 231. A pluralityof inlet apertures 201a, preferably four in number are formed around theouter sidewall of the manifold insert 201, and communicate through acommon central passageway with the upstream pressure port 232, therebyfacilitating accurate measurement of the pressure within the expiratoryflowpath 206 at that location.

An exhalation differential pressure transducer 70 (shown in FIG. 2) maybe located within the housing or enclosure of the ventilator 10. Theexhalation differential pressure transducer 70 is connected by way oftubing to the first and third pressure port tubing connectors 240 and235 so as to continuously measure and provide the controller 12 with thedifference between pressure upstream (P1) and pressure downstream (P2)of the flow transducer 230. The difference in pressure determined by theexhalation differential pressure transducer 70 is communicated to thecontroller, and the controller is operatively programmed to calculatethe actual flow rate at which expiratory gas is exiting the flow channel206. As will be recognized, the exhalation flow rate may be utilized bythe controller 12 for differing purposes such as triggering ofinitiation of the next inspiratory cycle.

Although the particular formation and mounting structure utilized forthe exhalation flow transducer 230 provides exceptional accuracy in mostsituations, the applicant has found that in certain circumstances, it isdesirable to eliminate any inaccuracies caused by manufacturing andassembly tolerances. As such, in the preferred embodiment, the specificoperational characteristics of each exhalation flow transducer 230,i.e., pressure differential for specific flow rates are measured forcalibration purposes and stored on a storage medium contained within theexhalation valve housing 18. In the preferred embodiment this specificcharacterization and calibration information is encoded on a radiofrequency transponder 203 of the type commercially available under theproduct name Tiris, manufactured by Texas Instruments, of Austin, Tex.The radio-frequency transponder 203 and its associatedtransmitter/receiver antenna 203a may be mounted within the exhalationvalve housing 200 as shown in FIG. 11c. Additionally, a radio frequencytransmitter/receiver is positioned within the ventilator system 10, suchthat upon command of the controller 12, the calibration andcharacterization data contained within the transponder 203 istransmitted via radio frequency to the receiver and stored within thecontroller 12. Subsequently, the controller 12 utilizes such storedcalibration and characterization data to specifically determineexpiratory flow rate based upon pressure differential values generatedby the differential pressure transducer 70.

F. A Preferred Auto Calibration Circuit

In the preferred embodiment, the ventilator device 14 of the ventilatorsystem 10 of the present invention incorporates an auto calibrationcircuit for periodic rezeroing of the system to avoid errors in thetidal volume or inspiratory flow delivered by the drag compressor 30.

In particular, as shown in FIG. 2 the preferred auto calibration circuitcomprises the following components:

a) a first auto-zero valve 74 on the line between the inlet 32 of thecompressor 30 and the differential pressure transducer 36;

b) a second auto-zero valve 76 on the line between the first pressureport of the exhalation valve 18 and the first pressure (P1) side of theexhalation differential pressure transducer 70;

c) a third auto-zero valve 80 on the line between the second pressure(P2) port 234 of the exhalation valve 18 and the second pressure (P2)side of the exhalation differential pressure transducer 70;

d) a fourth auto-zero valve 78 on the line between the outlet port 34and the differential pressure transducer 36; and

e) and a fifth auto-zero valve 72 on the line between the airwaypressure port 241 and the airway pressure transducer 68.

Each of the auto-zero valves 72, 74, 76, 78, 80 is connected to thecontroller 12 such that, at selected time intervals during theventilatory cycle, the controller 12 may signal the auto-zero valves 72,74, 76, 78, 80 to open to atmospheric pressure. While the auto-zerovalve 72, 74, 76, 78, 80 are open to atmospheric pressure, thecontroller 12 may re-zero each of the transducers 36, 68, 70 to whichthe respective auto-zero valve 72, 74, 76, 80 are connected. Suchperiodic re-zeroing of the pressure transducers 36, 68 and 70 willcorrect any baseline (zero) drift which has occurred during operation.

Ventilator Operation

With the structure defined, the basic operation of the ventilator system10 of the present invention may be described. As will be recognized, theparticular ventilatory mode selected by a technician may be input to thecontroller 12 via the input controls upon the display 380. Additionally,the technician must attach the inspiratory and exhalation tubing circuitto the patient PT as illustrated in FIG. 1.

Prior to initiation of patient ventilation, the controller 12 initiatesits auto calibration circuit and system check to insure that all systemparameters are within operational specifications. Subsequently,inspiration is initiated wherein the controller 12 rapidly acceleratesthe drag compressor 30. During such acceleration, air is drawn throughthe filter 50, accumulator 54 and supplied to the patient PT, via line22. During such inspiratory phase, the controller 12 monitors thepressure drop across the compressor 30, via pressure transducer 36, andthe rotational speed of the rotor 104. This data is then converted toflow by the controller 12 via the turbine characterization table toinsure that the proper flow and volume of inspiratory gas is deliveredto the patient PT. Additionally, during such inspiratory phase, theexhalation valve 18 is maintained in a closed position. In thoseapplications where oxygen blending is desired, the controller 12additionally opens selected ones of the solenoid valve 52a, 52b, 52c,52d and 52e, in timed sequence to deliver a desired volume of oxygen tothe accumulator 54, which is subsequently delivered to the patient PTduring inspiratory flow conditions.

When inspiratory flow is desired to be terminated, the controller 12rapidly stops or decelerates the drag compressor 30 to a basalrotational speed, and the patient is free to exhale through exhalationline 66 and through the exhalation valve 18. Depending upon desiredventilation mode operation, the controller 12 monitors the exhalationpressure, via pressure transducer 68 connected to the airway passage andadjusts the position of the valve relative the valve seat within theexhalation valve 18 to maintain desired airway pressures.Simultaneously, the controller 12 monitors the pressure differentialexisting across the exhalation flow transducer 230 via exhalationpressure transducer 70 to compute exhaled flow. This exhaled flow isused to compute exhaled volume and to determine a patient trigger. Whena breath is called for either through a machine or patient trigger, thecontroller initiates a subsequent inspiratory flow cycle with subsequentoperation of the ventilator system 10 being repeated between inspiratoryand exhalation cycles.

Those skilled in the art will recognize that differing ventilationmodes, such as intermittent mandatory ventilation (IMV), synchronizedintermittent mandatory ventilation (SMIV) controlled mechanicalventilation (CMV) and assist control ventilation (A/C), are allavailable modes of operation on the ventilator 10 of the presentinvention. Further those skilled in the art will recognize that byproper selection of control inputs to the ventilator 10, all modernbreath types utilized in clinical practice, may be selected, such asmachine cycled mandatory breath, machine cycled assist breath, patientcycled supported breath, patient cycled spontaneous breath, volumecontrolled mandatory breaths, volume controlled assist breaths, pressurecontrolled breaths, pressure support breaths, sigh breaths, proportionalassist ventilation and volume assured pressure support.

What is claimed is:
 1. An exhalation valve for controlling theexpiratory gas flow from a mammalian patient, said exhalation valvecomprising:a housing defining an expiratory gas flow passagewaytherethrough; an annular valve seat formed within said expiratory gasflow passageway; an annular diaphragm movably disposed within said gasflow passageway, in juxtaposition to said annular valve seat, saiddiaphragm being variably movable back and forth to various positionsbetween and including:i) a fully closed position wherein said diaphragmis firmly seated against said annular valve seat to prevent gas fromflowing through said passageway; and ii) a fully open position whereinsaid diaphragm is retracted away from said annular valve seat so as topermit substantially unrestricted flow of expiratory gas through saidpathway; an elongate actuation shaft having a proximal end and a distalend, the distal end of said actuation shaft being contactable with saiddiaphragm, and said actuation shaft being axially moveable back andforth to control the positioning of said diaphragm between said fullyclosed and said fully open positions; an electrical induction coillinked to said actuation shaft such that a decrease in the currentpassing into said induction coil will cause said shaft to advance in thedistal direction and an increase in the current passing into saidinduction coil will cause said shaft to retract in the proximaldirection; means for determining the flow rate of expiratory gas passingout of said exhalation valve; means for determining airway pressure; amicroprocessor controller connected to said means for determining airwaypressure, said controller being provided with a positive expiratorypressure setting, and said controller being connected to said inductioncoil and adapted to emit control signals to said induction coil tocontrol the movement of said actuation shaft in response to the currentairway pressure, thereby maintaining the present amount of positiveexpiratory pressure; a radio frequency transponder containing flowcharacterization data specific for said exhalation valve for the meansfor determining the flow rate of expiratory gas passing out of saidexhalation valve; said controller being further connected to said meansfor determining the flow rate of expiratory gas passing out of saidexhalation valve and being equipped to receive radio frequency input ofthe characterization data contained in the radio frequency transponder,and to utilize such data to determine the instant flow rate ofexpiratory gas passing out of said exhalation valve.
 2. The exhalationvalve of claim 1 wherein said controller is located remote from, saidexhalation valve.
 3. The exhalation valve of claim 1 wherein saidcontroller is further adapted to receive input signals from said meansfor determining the flow rate at which expiratory gas is passingoutwardly through said expiratory gas flow passageway, and for emittingcontrol signals to said induction coil to fully close said diaphragmwhen said flow rate has fallen to a predetermined basal level, thussignifying the end of the expiratory phase.
 4. An exhalation valvecomprising:a) a housing defining a first exhalation passageway throughwhich expiratory gas may outflow in a first direction; b) a valve seatformed within said passageway; c) a diaphragm having a front side and aback side, said diaphragm being sized and configured such that the frontside thereof may abut against said valve seat to thereby block the flowof gas through said exhalation passageway, said diaphragm being moveableback and forth between;i) a first position wherein said diaphragm isfully retracted from said valve seat to permit unrestricted flow throughsaid passageway; ii) a second position wherein said diaphragm is seatedon said valve seat to block flow through said passageway; iii) a rangeof intermediate positions between said first and second positionswherein said diaphragm will cause varying degrees of restriction of theflow through said passageway; d) an elongate shaft having a first endand a second end, the first end of said shaft being adjacent to the backside of said diaphragm, said shaft being axially moveable back and forthbetween;i) a first position wherein the first end of said shaft is at alocation which will retain said diaphragm in its first position; ii) asecond position wherein the first end of said shaft is at a locationwhich will allow said diaphragm to move to its second position; and,iii) a range of intermediate positions wherein said shaft is at alocation which will allow said diaphragm to move to one of itsintermediate positions; e) an electrical induction coil slidably mountedwithin said housing so as to move back and forth in response to changesin current applied to the coil, said coil consisting essentially ofmultiple spirally wound contiguous convolutions of wire upon which arigidifying coating has been applied to hold said wire in a closelycoiled substantially cylindrical configuration without an internalsupport structure; f) a mounting spider connecting said shaft to saidcoil, said spider configured to hold said shaft in co-axial alignmentwith the longitudinal axis of the coil, with the first end of the shaftprotruding toward the back side of said diaphragm such that, when thecoil moves forward, said shaft will move forward toward said first shaftposition, and when said coil moves rearward, said shaft will beretracted toward said second shaft position.
 5. The exhalation valve ofclaim 4 wherein the front surface of said diaphragm is planar andwherein said valve seat is angled relative to the plane of the frontsurface of the diaphragm such that, when said diaphragm is moving intosaid first diaphragm position, the front side of said diaphragm willinitially contact only one side of said valve seat and will subsequentlymove into contact with the remainder of said valve seat.
 6. Anexhalation valve comprising:a) a housing defining a first exhalationpassageway through which expiratory gas may outflow in a firstdirection; b) a valve seat formed within said passageway; c) a diaphragmhaving a front side and a back side, said diaphragm being sized andconfigured such that the front side thereof may be abut against saidvalve seat to thereby block the flow of gas through said exhalationpassageway, said diaphragm being moveable back and forth between a firstposition wherein said diaphragm is fully retracted from said valve seatto permit unrestricted flow through said passageway; a second positionwherein said diaphragm is seated on said valve seat to block flowthrough said passageway; and a range of intermediate positions betweensaid first and second positions wherein said diaphragm will causevarying degrees of restriction of flow through said passageway; d) anelongate shaft having a first end and a second end, the first end ofsaid shaft being adjacent to the back side of said diaphragm, said shaftbeing axially moveable back and forth between a first position whereinthe first end of said shaft is at a location which will retain saiddiaphragm in its first position; a second position wherein the first endof said shaft is at a location which will allow said diaphragm to moveto its second position; and range of intermediate positions wherein saidshaft is at a location which will allow said diaphragm to move to one ofits intermediate positions; e) an electrical induction coil slidablymounted within said housing so as to move back and forth in response tochanges in current applied to the coil, said coil consisting essentiallyof multiple convolutions of wire upon which a rigidifying coating hasbeen applied to hold said wire in a closely coiled substantiallycylindrical configuration; f) a mounting spider connecting said shaft tosaid coil, said spider configured to hold said shaft in co-axialalignment with the longitudinal axis of the coil, with the first end ofthe shaft protruding toward the back side of said diaphragm such that,when the coil moves forward, said shaft will move forward toward saidfirst shaft position, and when said coil moves rearward, said shaft willbe retracted toward said second shaft position; g) a pliable dustbarrier disposed between said valve seat and said induction coil, saidpliable dust barrier being sealed to the surrounding housing to preventparticulate matter from passing around said shaft and into saidinduction coil, said dust barrier being in contact with said shaft andbeing sufficiently flexible to move back and forth in accordance withaxial movement of said shaft.
 7. The exhalation valve of claim 6 whereinsaid dust barrier comprises an elastomeric boot.
 8. The exhalation valveof claim 6 wherein at least one vent hole is formed in said exhalationvalve to prevent the creation of pressure on at least one side of saiddust barrier as said dust barrier flexes back and forth.
 9. Anexhalation valve comprising:a housing defining an expiratory gas flowpath connectable to a mammalian patient such that expiratory gas exhaledby the patient will pass through said flow path in a first direction; avalve associated with said flow path to permit gas exhaled by thepatient to pass through said flow path in said first direction, but toprevent gas from being drawn through said flow path in a seconddirection, opposite said first direction, when said patient inhales; aflow measuring apparatus for monitoring the flow rate of expiratory gaspassing through said exhalation valve; and specific flow-pressurecalibration information for the flow measuring apparatus stored on astorage medium contained within the exhalation valve housing.
 10. Theexhalation valve of claim 9 wherein said flow measuring apparatuscomprises:a flapper disposed transversely within said flow path, saidflapper being constructed such that at least a portion of said flapperwill deflect in a first direction when exhaled gas is passed throughsaid flow path in said first direction, the extent of flapper deflectionbeing variable with the flow rate of gas passing through the exhalationvalve, said flapper thereby creating a dynamic flow restricting orificewithin said flow path; means for determining gas pressure within saidflow path upstream of said flapper; means for determining gas pressurewithin said flow path downstream of said flapper; means for determiningthe then-current flow rate of gas passing through said exhalation valve,based on the difference in the pressures measured upstream anddownstream of said flapper.
 11. The exhalation valve device of claim 10wherein said flapper is mounted within a flapper assembly whichcomprises:a sheet of pliable material having a first side, a second sideand an outer peripheral edge, a semi-annular cut being formed in saidsheet to divide said sheet into i) an outer peripheral portion which isoutboard of said cut and ii) an inner flapper portion which is inboardof said cut, and which remains attached on one side thereof to thesurrounding peripheral portion of said sheet, said inner flapper portionof said sheet being thereby deflectable back and forth while the outerperipheral portion of said sheet is held in substantially stationaryposition; a first frame member having a central aperture formed therein,said first frame member being juxtaposed to the first side of said sheetsuch that said first frame member is in contact with the first side ofthe peripheral portion of said sheet and the central aperture of saidfirst frame member surrounds the first side of the flapper portion ofsaid sheet; a second frame member having a central aperture formedtherein, said second frame member being juxtaposed to the second side ofsaid sheet such that said frame member abuts against the second side ofthe peripheral portion of said sheet, and the central aperture of saidsecond frame member surrounds the second side of the flapper portion ofsaid sheet; said first and second frame members thereby holding theperipheral portion of said sheet in a substantially fixed positionbetween said frame members while the flapper portion of said sheetextends transversely into the space between the axially alignedapertures of said frame members and is deflectable back and forththerein.
 12. The exhalation valve device of claim 11 wherein saidflapper assembly is positioned transversely within the flow path of saidexhalation valve and is held in such position by engagement to thesurrounding exhalation valve housing.
 13. The exhalation valve device ofclaim 11 further comprising:a cushioning washer and a third frame memberdisposed on at least one of the first and second frame member which abutagainst the same so as to evenly distribute stresses applied to saidsheet by said frame members.
 14. The exhalation valve device of claim 13wherein said cushioning washer comprises an elastomeric materialdisposed on said third frame member.
 15. The exhalation valve device ofclaim 9 wherein said storage medium comprises a radio-frequencytransponder.
 16. The exhalation valve device of claim 9 wherein thecharacterization information stored on said storage medium comprises adata base of predetermined pressure differences for specific flow ratesof said exhalation valve.
 17. The exhalation valve device of claim 9wherein the information stored on said storage medium comprises anequation for calculating specific flow rates base on measured pressuredifferentials for that exhalation valve.